We're used to seeing Hollywood blockbusters as by-products of toy, game and comic franchises but there's something especially blatant about The Lego Movie. As one of its creators freely admits, the title sets you up for a 90-minute toy commercial.

And despite its many pleasures, the film never quite succeeds in banishing that thought. The problem is the pace. It never lets up. The directors, Phil Lord and Christopher Miller, seem so spooked by fears of their young audience's short attention span that some of their best touches go by in a blur. The film is bursting with ideas. It seems that Lego insisted on them. In deference to the playful spirit of inquiry that helped the company grow from its beginnings in a Danish carpenter's workshop in 1932, its chiefs wanted something in line with the brilliance of Toy Story. And they got it. Threaded between the fireworks are a string of clever jokes aimed at some of Hollywood's fondest cliches, together with a well-pitched storyline in praise of lateral thinking, but you don't get much time to dwell on them.

It's a classic theme. Lord Business (Will Ferrell), the tyrannical tycoon who runs Legoland, has imbued the place and its citizens with a crippling sense of conformity. Emmet (Chris Pratt), a construction worker, has become so used to obeying the rules that he can't imagine living any other way. Then he tumbles into a deep hole on a building site and is treated, like Lewis Carroll's Alice, to an entirely different view of the world.

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During his underground adventure, he meets a new mentor, Vitruvius (Morgan Freeman), an ancient wizard convinced that Emmet is the "special" - the long-awaited saviour, who's destined to overthrow the ruthless regime of Lord Business and usher in a new age of freedom and innovation. So it's a plot very much in line with the teachings of Joseph Campbell, whose work on comparative mythologies and their heroes has inspired so many Hollywood scripts. But this one tweaks them a bit. Vitruvius is no Obi-Wan Kenobi. His prophesies are the product of guesswork rather than wisdom, and Emmet doesn't come into his own as a hero until he's mastered the art of delegation.

Even so - or rather, because of his reluctance to play the great man - he's made a big impression on certain political commentators in the US. A Huffington Post columnist recently decided that he could give the left some crucial lessons about the power of collective action, and that President Obama, in particular, could learn a thing or two from him. And if you find something deeply depressing in the idea of the American president taking advice from a Lego figure, you're not alone.

Emmet's adventures take us on a comprehensive tour of Legoland's diverse districts. We visit the city, the country, the Old West and the medieval era in company with Lego versions of Batman, Gandalf, Dumbledore, Wonder Woman, Superman and an assortment of Star Wars characters - which, in itself, is a tribute to collective corporate action. Emmet also develops a crush on his feisty guide, Wyldstyle (Elizabeth Banks), and Liam Neeson enjoys himself hugely giving voice to a cop who possesses a good and a bad side and switches between them at a bewildering rate.

The animation, by Australia's Animal Logic, is superb. Elaborate Lego worlds are constructed, destroyed and re-assembled in even more fabulous configurations as you watch. Despite the speed at which the whole thing unfolds, the figures move in a way that's entirely in keeping with their brick-like forms.

With all this going for the film, you can understand why Lego should be so pleased with it and why it's already had such box-office success internationally - but its relentless action and pounding soundtrack sent me out feeling battered rather than uplifted and the nine-year-old who came with me had the same response. If only Lord and Miller had demonstrated more faith in the wonders they were putting up on screen, it would all have been a joy.